Catheter display showing tip angle and pressure

ABSTRACT

A method for displaying information includes receiving a measurement with respect to an invasive probe inside a body of a subject of at least one probe parameter, selected from a group of parameters consisting of a bend angle of the probe and a pressure on the probe. Responsively to the measurement, an icon is displayed on a display screen representing the at least one probe parameter for viewing by an operator of the probe.

FIELD OF THE INVENTION

The present invention relates generally to invasive medical devices, andspecifically to methods and devices for displaying characteristics of aprobe, such as a catheter, inside the body of a patient.

BACKGROUND OF THE INVENTION

In some diagnostic and therapeutic techniques, a catheter is insertedinto a chamber of the heart and brought into contact with the innerheart wall. In such procedures, it is generally important that thedistal tip of the catheter engages the endocardium with sufficientpressure to ensure good contact. Excessive pressure, however, may causeundesired damage to the heart tissue and even perforation of the heartwall.

For example, in intracardiac radio-frequency (RF) ablation, a catheterhaving an electrode at its distal tip is inserted through the patient'svascular system into a chamber of the heart. The electrode is broughtinto contact with a site (or sites) on the endocardium, and RF energy isapplied through the catheter to the electrode in order to ablate theheart tissue at the site. Proper contact between the electrode and theendocardium during ablation is necessary in order to achieve the desiredtherapeutic effect without excessive damage to the tissue.

A number of patent publications describe catheters with integratedpressure sensors for sensing tissue contact. As one example, U.S. PatentApplication Publication 2007/0100332, whose disclosure is incorporatedherein by reference, describes systems and methods for assessingelectrode-tissue contact for tissue ablation. An electro-mechanicalsensor within the catheter shaft generates electrical signalscorresponding to the amount of movement of the electrode within a distalportion of the catheter shaft. An output device receives the electricalsignals for assessing a level of contact between the electrode and atissue.

As another example, U.S. Pat. No. 6,695,808, whose disclosure isincorporated herein by reference, describes apparatus for treating aselected patient tissue or organ region. A probe has a contact surfacethat may be urged against the region, thereby creating contact pressure.A pressure transducer measures the contact pressure. This arrangement issaid to meet the needs of procedures in which a medical instrument mustbe placed in firm but not excessive contact with an anatomical surface,by providing information to the user of the instrument that isindicative of the existence and magnitude of the contact force.

Other catheters with pressure sensors are described in U.S. Pat. No.6,241,724 and U.S. Pat. No. 6,915,149, whose disclosures areincorporated herein by reference.

PCT International Publication WO 2007/067938, whose disclosure isincorporated herein by reference, describes a method for displayingcatheter electrode-tissue contact in an electro-anatomic mapping andnavigation system. The system provides an indication to the physicianconcerning the electrical coupling of an electrode, such as an ablativeor mapping electrode, with a patient. The indication may be provided bychanging the color or other display characteristics of the electrode onthe navigation system display or by way of providing a waveformindicating the electrode coupling. This manner of providing electrodecoupling information is said to minimize physician distraction.

SUMMARY OF THE INVENTION

The embodiments of the present invention that are described hereinbelowprovide novel means and methods for displaying parameters associatedwith the quality of engagement between an invasive probe and tissuewithin the body of a subject. This sort of display can assist theoperator of the probe in visualizing the situation of the probe and thusin ensuring the effectiveness and safety of diagnostic and/ortherapeutic procedures that are performed using the probe.

An embodiment of the present invention provides a method for displayinginformation. The method includes receiving a measurement with respect toan invasive probe inside a body of a subject of at least one probeparameter, selected from a group of parameters consisting of a bendangle of the probe and a pressure on the probe. Responsively to themeasurement, an icon is displayed on a display screen representing theat least one probe parameter for viewing by an operator of the probe.

In some embodiments, the probe includes a distal tip that bends at aresilient joint, and receiving the measurement includes measuring adeformation of the joint due to engagement of tissue in the body by thedistal tip. In a disclosed embodiment, the probe includes a catheter,which is inserted into a chamber of a heart of the subject and engagesmyocardial tissue. The method may include applying energy via the distaltip so as to ablate the myocardial tissue, wherein the operator controlsapplication of the energy responsively to the icon. Additionally oralternatively, measuring the deformation includes sensing both thedeformation of the joint and a position of the probe within the body bytransmitting and receiving one or more magnetic fields.

Typically, displaying the icon includes positioning the icon on thedisplay screen so as to represent a location of the probe within thebody. Positioning the icon may include locating the icon on the displayscreen relative to a map of a surface of an organ of the body, andwherein receiving the measurement includes measuring the pressurebetween the probe and the surface.

In a disclosed embodiment, displaying the icon includes presenting theicon so as to show both the bend angle and the pressure, wherein theicon is articulated to show the bend angle and is colored to representthe pressure.

There is also provided, in accordance with an embodiment of the presentinvention, apparatus for performing a medical procedure, including adisplay screen arranged for viewing by an operator of an invasive probeinside a body of a subject. A processor is coupled to receive ameasurement with respect to the invasive probe of at least one probeparameter, selected from a group of parameters consisting of a bendangle of the probe and a pressure on the probe, and to display an iconon the display screen, responsively to the measurement, representing theat least one probe parameter.

There is additionally provided, in accordance with an embodiment of thepresent invention, a computer software product, including acomputer-readable medium in which program instructions are stored, whichinstructions, when read by a computer, cause the computer to receive ameasurement with respect to an invasive probe inside a body of a subjectof at least one probe parameter, selected from a group of parametersconsisting of a bend angle of the probe and a pressure on the probe, andto display, responsively to the measurement, an icon on a display screenrepresenting the at least one probe parameter for viewing by an operatorof the probe.

The present invention will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, pictorial illustration of a catheter-basedmedical system, in accordance with an embodiment of the presentinvention;

FIG. 2 is a schematic detail view showing the distal tip of a catheterin contact with endocardial tissue, in accordance with an embodiment ofthe present invention; and

FIG. 3 is a schematic representation of a display screen including anicon corresponding to a catheter tip, in accordance with an embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic, pictorial illustration of a system 20 for cardiaccatheterization, in accordance with an embodiment of the presentinvention. System 20 may be based, for example, on the CARTO® system,produced by Biosense Webster Inc. (Diamond Bar, Calif.). This systemcomprises an invasive probe in the form of a catheter 28 and a controlconsole 34. In the embodiment described hereinbelow, it is assumed thatcatheter 28 is used in ablating endocardial tissue, as is known in theart. Alternatively, the catheter may be used mutatis mutandis, for othertherapeutic and/or diagnostic purposes in the heart or in other bodyorgans.

An operator 26, such as a cardiologist, inserts catheter 28 through thevascular system of a patient 24 so that a distal end 30 of the catheterenters a chamber of the patient's heart 22. The operator advances thecatheter so that the distal tip of the catheter engages endocardialtissue at a desired location or locations. Catheter 28 is typicallyconnected by a suitable connector at its proximal end to console 34. Theconsole comprises a radio frequency (RF) generator 40, which supplieshigh-frequency electrical energy via the catheter for ablating tissue inthe heart at the locations engaged by the distal tip, as describedfurther hereinbelow. Alternatively, the catheter and system may beconfigured to perform ablation by other techniques that are known in theart, such as cryo-ablation. Further alternatively or additionally, thecatheter and system may be used to perform other sorts of therapeuticand/or diagnostic procedures, such as electro-anatomical mapping.

Console 34 uses a position sensing technique to determine positioncoordinates of distal end 30 of catheter 28 inside heart 22. In thepresent embodiment, it is assumed that the console uses magneticposition sensing, which is also used in deriving angle and pressureinformation with respect to the distal end, as described furtherhereinbelow. Alternatively or additionally, the principles of thepresent invention may be applied using other position sensing andpressure sensing techniques, as are known in the art.

For the purpose of magnetic position sensing, a driver circuit 38 inconsole 34 drives field generators 32 to generate magnetic fields withinthe body of patient 24. Typically, the field generators comprise coils,which are placed below the patient's torso at known positions externalto the patient. These coils generate magnetic fields in a predefinedworking volume that contains heart 22. A magnetic field sensor withindistal end 30 of catheter 28 (not shown in the figures) generateselectrical signals in response to these magnetic fields. A signalprocessor 36 processes these signals in order to determine the positioncoordinates of the distal end, typically including both location andorientation coordinates. This method of position sensing is implementedin the above-mentioned CARTO system and is described in detail in U.S.Pat. Nos. 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612 and6,332,089, in PCT Patent Publication WO 96/05768, and in U.S. PatentApplication Publications 2002/0065455 A1, 2003/0120150 A1 and2004/0068178 A1, whose disclosures are all incorporated herein byreference.

Processor 36 typically comprises a general-purpose computer, withsuitable front end and interface circuits for receiving signals fromcatheter 28 and controlling the other components of console 34. Theprocessor may be programmed in software to carry out the functions thatare described herein. The software may be downloaded to console 34 inelectronic form, over a network, for example, or it may be provided ontangible media, such as optical, magnetic or electronic memory media.Alternatively, some or all of the functions of processor 36 may becarried out by dedicated or programmable digital hardware components.

Based on the signals received from catheter 28 and other components ofsystem 20, processor 36 drives a display 42 to give operator 26 visualfeedback regarding distal end 30 of catheter 28 in the patient's body,as well as status information and guidance regarding the procedure thatis in progress. The visual feedback shows the pressure on the distalend, as well as the bend angle of the distal tip of the catheter, as isdescribed further hereinbelow with reference to FIG. 3.

Alternatively or additionally, system 20 may comprise an automatedmechanism for maneuvering and operating catheter 28 within the body ofpatient 24. Such mechanisms are typically capable of controlling boththe longitudinal motion (advance/retract) of the catheter and transversemotion (deflection/steering) of the distal end of the catheter. Somemechanisms of this sort use DC magnetic fields for this purpose, forexample. In such embodiments, processor 36 generates a control input forcontrolling the motion of the catheter based on the signals provided bythe magnetic field sensor in the catheter. As noted earlier, thesesignals are indicative of both the position of the distal end of thecatheter and force exerted on the distal end. In this case, the pressureand bend angle shown on display 42 may be used by a human operator inmonitoring the status and progress of the automated procedure.

FIG. 2 is a schematic sectional view of a chamber of a heart 22, showingdistal end 30 of catheter 28 inside the heart, in accordance with anembodiment of the present invention. The catheter comprises an insertiontube 60, which is typically inserted into the heart percutaneouslythrough a blood vessel, such as the vena cava or the aorta. An electrode50 on a distal tip 52 of the catheter engages endocardial tissue 70.Pressure exerted by the distal tip against the endocardium deforms theendocardial tissue locally, so that electrode 50 contacts the tissueover a relatively large area. In the pictured example, the electrodeengages the endocardium at an angle, rather than head-on. Distal tip 52therefore bends at a resilient joint 56 relative to the distal end ofinsertion tube 60 of the catheter. The bend may facilitate optimalcontact between the electrode and the endocardial tissue.

Because of the elastic quality of joint 56, the angle of bending and theaxial displacement of the joint are proportional to the pressure exertedby tissue 70 on distal tip 52 (or equivalently, the pressure exerted bythe distal tip on the tissue). Measurement of the deformation of thejoint, in terms of bend angle and axial displacement, thus gives anindication of this pressure. The pressure indication may be used byoperator 26 of system 20 in ensuring that the distal tip is pressingagainst the endocardium firmly enough to give the desired therapeutic ordiagnostic result, but not so hard as to cause undesired tissue damage.

Various techniques may be used in measuring the bend angle and pressureexerted on distal tip 52. Components and methods that may be used forthis purpose are described, for example, in U.S. patent application Ser.No. 11/868,733, filed Oct. 8, 2007, which is assigned to the assignee ofthe present patent application and whose disclosure is incorporatedherein by reference. This patent application describes a catheter whosedistal tip is coupled to the distal end of the catheter insertion tubeby a spring-loaded joint (such as joint 56), which deforms in responseto pressure exerted on the distal tip when it engages tissue. A magneticposition sensing assembly within the probe, comprising coils on oppositesides of the joint, senses the position of the distal tip relative tothe distal end of the insertion tube. Changes in this relative positionare indicative of deformation of the spring and thus give an indicationof the pressure.

Joint 56 may comprise a superelastic coupling member, as described inU.S. patent application Ser. No. 12/134,592, filed Jun. 6, 2008.Alternatively, the coupling member may comprise a coil spring or anyother suitable sort of resilient component with the desired flexibilityand strength characteristics. U.S. patent application Ser. No.12/327,226, filed Dec. 3, 2008, describes an arrangement of magneticcoils within the distal end of the catheter that can be used in sensingthe tip angle and pressure with enhanced accuracy. Both of these twopatent applications are assigned to the assignee of the present patentapplication, and their disclosures are incorporated herein by reference.

FIG. 3 is a schematic representation of a map 80 of a heart chamber,which includes an icon 84 corresponding to distal end 30 of catheter 28,in accordance with an embodiment of the present invention. A map of thissort is typically presented on display 42, as an aid to operator 26 invisualizing the distal end of the catheter within heart 22. The mapincludes a graphical representation of an inner surface 82 of the heartchamber in which the distal end of the catheter is located. (Surface 82may be fully reconstructed, as shown in FIG. 3, or only partiallyreconstructed.) The position of icon 84 relative to surface 82 gives theoperator an indication of the location of the actual distal end of thecatheter in the heart chamber.

Icon 84 shows not only the location of distal end 30, but also angularand pressure characteristics. In the example shown in FIG. 3, the iconis articulated to show the measured bend angle of distal tip 52 relativeto insertion tube 60. If the operator sees that the distal tip of thecatheter is sharply bent, for example, he or she may readjust theposition of the catheter before continuing with a diagnostic ortherapeutic procedure, such as ablating the heart tissue.

Furthermore, at least a portion 86 of the icon may be colored(represented in the figure by hatching) to indicate the pressure. Forexample, green coloring may indicate that the pressure is within thecorrect pressure range for RF ablation, while red indicates too muchpressure, and blue indicates too little. The pressure ranges may bepreset, or they may be adjusted by the operator. In either case, theoperator will then apply the RF energy only when the pressure is withinthe range that will give the desired therapeutic result.

The graphical display of pressure and bend angle by icon 84 gives theoperator additional visual information that is not provided by displaytechniques that are known in the art. This additional information can beuseful as a complement to or in place of measurement of electrode/tissueelectrical contact resistance. The pressure and/or angle display itselfis important, for example, under the following circumstances:

-   -   When touching scarred myocardium, the electrical contact        resistance will not accurately reflect pressure, and therefore        direct pressure measurement is needed.    -   When the catheter touches the heart wall sideways (along the        length of the catheter), the electrical contact resistance may        be low, because the contact area is large, even though the        pressure exerted by the catheter on the heart wall is low. The        pressure and/or angle display of FIG. 3 allows the operator to        detect and rectify this sort of situation.    -   Similarly, when a catheter touches a trabeculated wall, the        electrical contact resistance may be low even if little or no        pressure is applied. Direct pressure measurement enables the        operator to detect and rectify this sort of situation, as well.

Although icon 84 in FIG. 3 represents both tip angle and pressureparameters, in addition to location of the catheter tip, the examplesabove show that it can be useful to display either the angle or thepressure by itself. Alternatively or additionally, one or both of theangle and pressure measurements may be displayed together with ameasurement of electrical contact resistance or other parameters.Furthermore, although FIG. 3 shows a particular mode of graphicalrepresentation, other techniques for displaying angle and pressure datawill be apparent to those skilled in the art and are considered to bewithin the scope of the present invention. The display techniques thatare described or suggested hereinabove may be used not only in cardiaccatheterization procedures, but also in other types of invasivediagnostic and therapeutic applications.

It will thus be appreciated that the embodiments described above arecited by way of example, and that the present invention is not limitedto what has been particularly shown and described hereinabove. Rather,the scope of the present invention includes both combinations andsubcombinations of the various features described hereinabove, as wellas variations and modifications thereof which would occur to personsskilled in the art upon reading the foregoing description and which arenot disclosed in the prior art.

1. A method for displaying information, comprising: receiving ameasurement with respect to an invasive probe inside a body of a subjectof at least one probe parameter, selected from a group of parametersconsisting of a bend angle of the probe and a pressure on the probe; andresponsively to the measurement, displaying an icon on a display screenrepresenting the at least one probe parameter for viewing by an operatorof the probe.
 2. The method according to claim 1, wherein the probecomprises a distal tip that bends at a resilient joint, and whereinreceiving the measurement comprises measuring a deformation of the jointdue to engagement of tissue in the body by the distal tip.
 3. The methodaccording to claim 2, wherein the probe comprises a catheter, which isinserted into a chamber of a heart of the subject and engages myocardialtissue.
 4. The method according to claim 3, and comprising applyingenergy via the distal tip so as to ablate the myocardial tissue, whereinthe operator controls application of the energy responsively to theicon.
 5. The method according to claim 2, wherein measuring thedeformation comprises sensing both the deformation of the joint and aposition of the probe within the body by transmitting and receiving oneor more magnetic fields.
 6. The method according to claim 1, whereindisplaying the icon comprises positioning the icon on the display screenso as to represent a location of the probe within the body.
 7. Themethod according to claim 6, wherein positioning the icon compriseslocating the icon on the display screen relative to a map of a surfaceof an organ of the body, and wherein receiving the measurement comprisesmeasuring the pressure between the probe and the surface.
 8. The methodaccording to claim 1, wherein displaying the icon comprises presentingthe icon so as to show both the bend angle and the pressure.
 9. Themethod according to claim 8, wherein the icon is articulated to show thebend angle and is colored to represent the pressure.
 10. An apparatusfor performing a medical procedure, comprising: a display screenarranged for viewing by an operator of an invasive probe inside a bodyof a subject; and a processor, which is coupled to receive a measurementwith respect to the invasive probe of at least one probe parameter,selected from a group of parameters consisting of a bend angle of theprobe and a pressure on the probe, and to display an icon on the displayscreen, responsively to the measurement, representing the at least oneprobe parameter.
 11. The apparatus according to claim 10, and comprisingthe invasive probe, wherein the probe comprises a distal tip that bendsat a resilient joint, and wherein the processor is configured to measurea deformation of the joint due to engagement of tissue in the body bythe distal tip.
 12. The apparatus according to claim 11, wherein theprobe comprises a catheter, for insertion into a chamber of a heart ofthe subject so as to engage myocardial tissue.
 13. The apparatusaccording to claim 12, wherein the catheter is configured to applyenergy via the distal tip so as to ablate the myocardial tissue, whereinthe operator controls application of the energy responsively to theicon.
 14. The apparatus according to claim 11, and comprising at leastone magnetic field generator for generating a magnetic field in avicinity of the probe, wherein the processor is configured to measureboth the deformation of the joint and a position of the probe within thebody responsively to the magnetic field.
 15. The apparatus according toclaim 10, wherein the processor is configured to position the icon onthe display screen so as to represent a location of the probe within thebody.
 16. The apparatus according to claim 15, wherein the processor isconfigured to generate a map of a surface of an organ of the body, tolocate the icon on the display screen relative to the map, and tomeasure the pressure between the probe and the surface.
 17. Theapparatus according to claim 10, wherein the icon shows both the bendangle and the pressure.
 18. The apparatus according to claim 17, whereinthe icon is articulated to show the bend angle and is colored torepresent the pressure.
 19. A computer software product, comprising acomputer-readable medium in which program instructions are stored, whichinstructions, when read by a computer, cause the computer to receive ameasurement with respect to an invasive probe inside a body of a subjectof at least one probe parameter, selected from a group of parametersconsisting of a bend angle of the probe and a pressure on the probe, andto display, responsively to the measurement, an icon on a display screenrepresenting the at least one probe parameter for viewing by an operatorof the probe.